Musings on the science and art of gardening

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Archive | March 2017

Although red buckeye (Aesculus pavia) lacks the refined and symmetrical stature of commercially successful small ornamental trees, it makes up for it with an impressive show of 6- to 10-inch long salmon- to cherry-red flower spikes borne at the ends of its branches. These hummingbird magnets emerge in April and coincide with the spring migration of ruby-throated hummingbirds. The nectar also fortifies other pollinators including eastern tiger swallowtail butterflies, bumblebees, and carpenter bees.

In nature this large shrub to small tree (10 to 20 ft.) grows wild in floodplains and swamp forests throughout the southeast; however, I’ve seen it successfully cultivated en masse in woodland gardens, as accent or specimen plants in landscapes, and in downtown city parks

Once the flowers have faded I enjoy the dark green palmately compound leaves and smooth gray bark. Later in the season potato-shaped husks that arose from the flowers mature and split open in September and October to reveal 1 to 3 shiny brown nut-like seeds. The seeds are poisonous and avoided by most wildlife, but relished by squirrels.

Red buckeye checks out and goes dormant by September with no colorful fanfare. However, when provided with moist, partially shaded conditions, the leaves will turn yellow.

I accept the early departure of red buckeye as it disappears in my landscape. Its leafless branches receive quizzical looks from friends and passersby who typically ask: “Is it dead?” Despite its forlorn look in the fall and winter months, red buckeye will always have a place in my garden. Its flowers sustain my spirit and they nourish the bodies of well-traveled, winged pollinators.

Once upon a time the Bradford pear (Pyrus calleryana ‘Bradford’) was the darling of the nursery industry. Since its debut on the cover of American Nurseryman magazine on April 15, 1963, Bradford pear’s popularity soared as a street-tough tree that offered beauty and durability. In early spring Bradford pear trees erupted into bloom, these giant ovate snowballs of bright white flowers that were best admired from a distance because of their rotting fish aroma. The flowers, favored by honeybees, bumblebees and other pollinators oblivious to the stench, gave rise to leathery, dark glossy green leaves that “present[ed] a pleasing picture, particularly as they stir in the breeze and their wavy edges catch and reflect the sun’s rays,” according to the authors of the 1963 American Nurseryman article “Bradford ornamental pear—a promising shade tree.” In the fall the longlasting leaves exploded into shades of orange, red, and purple. The beauty of Bradford pear was matched by its unparalleled toughness: tolerance to drought, pollution, and pests, notably to fire blight, a devastating bacterial disease that injures and kills edible pears.

Bradford pear appeared to be the perfect ornamental street tree, but like kryptonite and Superman, Bradford pear’s Achille’s heel was its production of closely spaced upright branches. As these poorly attached branches grew and expanded in girth, the crown to split apart, often during snow-, ice-, and windstorms. It often happened to unpruned or poorly pruned trees when they reached 15 to 20 years of age.

In the past I counseled anyone who purchased a Bradford pear to buy a pruning saw as well. As described in the 1963 American Nurseryman article, the limbs of young trees must be selectively removed to produce branches with wider angles and stronger unions to develop a strong canopy.

To overcome this structural flaw, cultivars were developed that offered improved branching habits, such as ‘Aristocrat’ and ‘Chanticleer’, a 2005 Urban Tree of the Year by the Society of Municipal Arborists. Other cultivars were developed with narrower forms, such as ‘Capital‘, a U. S. National Arboretum release, that embodied the aesthetic and urban-tolerant traits of Bradford but offered applications in tight, confined locations.

This profusion of callery pear cultivars eventually led to another problem that had ecological consequences. In the past, Bradford pear rarely produced viable fruit because it’s self-infertile and cannot pollinate itself. With the widespread planting of cultivars that were differed slightly genetically, the barrier to fertility and subequent fruit production was overcome. In some cases the callery pear understock of a Bradford pear would sprout, flower, and provide pollen. The fruits were consumed and dispersed by starlings, robins, and other animals to open, disturbed habitats where the progeny formed dense thickets.

Callery pears mature early—flowering at 3 years of age–and is one of the first trees to bloom in early spring. It’s also one of the last trees to lose its leaves. Callery pears are resistant to insects and diseases and their thorny stems and branches discourage deer-browsing. Interestingly, the “Survivor Tree” at the 9/11 Memorial is a callery pear that survived the September 11, 2001 terror attacks at the World Trade Center. In the context of the Memorial, it serves as a symbol of survival, recovery, and resilience.

Some states in the mid-Atlantic, southeast and midwest regions have declared callery pear an invasive, self-sustaining species that dominates and disrupts native flora. In South Carolina callery pear (and Bradford pear) is considered an invasive species by the Southeast Exotic Pest Plant Council (SE-EPPC).

In the past I encouraged Bradford pear owners in our state to selectively prune the branches. Now that I witnessed large tracts of land throughout our state covered like a white fog in early spring, I encourage them to prune their trees at soil level.

The glorification and eventual demonization of Bradford pear is the result of our unwillingness to foster biodiversity in our urban environments. While we make our communities more livable for people, we don’t do the same for trees. We disregard decades of arboricultural research and practices and continue to shoe-horn trees into unsustainable 4 square ft. tree pits that are better suited for traffic lights, signs, and streetlights than trees. It’s the survival of the fittest, and only a handful of tree species can exist in these inhospitable conditions. Bradford pear is one of them. This monocultural approach that relies on a single or limited number of species or cultivars had already led to catastrophic losses in our urban forests as witnessed by the demise of American elms to Dutch elm disease and ashes to emerald ash borer. However, we continue to rely on a handful of nearly indestructible species and cultivars that thrive in wretched conditions. Crapemyrtle (Lagerstroemia indica cultivars and hybrids), Chinese elm (Ulmus parvifolia), sawtooth oak (Quercus acutissima), and Chinese pistache (Pistacia chinensis) have supplanted Bradford pear as street-tough urban warriors.

Because cities are responsible for 70% of the world’s greenhouse-gas emissions but comprise only 2% of the world’s land mass (Time; Dec. 26, 2016/Jan. 2, 2017), we rely on trees to assume a greater role as ecological engineers in our urban communities. It’s important that communities create growing conditions that support a diverse population of native and noninvasive adapted tree species that provide environmental services and not ecological messes.

Despite “season creep,” Nature reminded me today that Spring has not officially arrived yet. At 7:26 a.m. it’s 38 degrees F and snowing. Despite this wintry mix, I still have Spring fever. It reminds me of the ”More Cowbell” Saturday Night Live sketch with “famed producer Bruce Dickinson” played by Christopher Walken. I find myself saying: “I got a fever! And the only prescription…is to get outside and garden.”

Fill your prescription for Spring fever after this unexpected unpleasantness passes with this short “to do” list of gardening activities.

Edibles

Buy seed potatoes and cut them into egg-sized pieces containing one or two eyes. Allow the cuts to dry and callous for a day or two before planting. Plant them when the soil temperature remains above 50o

Set out transplants of broccoli, cabbage, and cauliflower as well, up to four weeks before the last spring freeze.

Vegetables that resent any root disturbance, such as cucumber, muskmelon, summer squash, and watermelon, should be sown in individual pots or peat pellets.

Sweet potatoes are started from “slips”—shoots that sprouted from last year’s crop. Purchase them as transplants or start your own by placing a sweet potato in a glass half-filled with water. Place it in bright light. Detach the plants from the mother root when they are 6 to 8 inches long, pot them up, and then plant them in the garden about three weeks after the last freeze.

Sow parsley and dill. To encourage parsley seeds to sprout more rapidly, soften the seeds by soaking them overnight in warm water. Refer to the Planting Chart — Dates to Plant in SC for more information (hgic.clemson.edu).

Bulbs

After flowering, the leaves of your spring-flowering bulbs will turn an unsightly yellow. Temper your urge to remove the leaves, or braid them into attractive ponytails. The bulbs need the leaves to harvest energy that’s channeled to the bulb for next year’s flowers.

Perennials and Ornamental Grasses

Dig up, divide, and replant established perennials if they’ve become too crowded and flowering has been sparse. Some fast-growing perennials need to be divided between one and three years after planting—these include aster, astilbe, beebalm, boltonia, garden mum, garden phlox, rudbeckia, Shasta daisy, and many others. To avoid interrupting flowering, dig up summer- and fall-blooming perennials when the new growth is a few inches high.

Divide ornamental grasses before new growth emerges. Cut back the old culms to within 4 to 6 inches of the ground and use a sharp shovel or large knife to slice one or more wedges out of the crown. Immediately plant them elsewhere.

Shrubs

Dense shrubs should not be planted close to the foundation or siding, or in front of foundation vents because they can obstruct air flow around and beneath your home, which can lead to moisture problems. Prune these shrubs or move them to another area in the landscape. If you move them to south- or west-facing walls to insulate your house from summer’s heat, keep them away from foundation vents and at least 4 feet from the foundation.

Keep shrubs away from the compressor on your split-system air conditioner. While the shade cast by the shrubs can reduce energy consumption, they should be planted far enough away so they won’t obstruct air flow or service.